WO2020201224A1

WO2020201224A1 - Selective coupling device for a collet chuck

Info

Publication number: WO2020201224A1
Application number: PCT/EP2020/058987
Authority: WO
Inventors: Davide Sarchi; Myriam MOSIMANN; Yann GATEAU
Original assignee: Bien-Air Holding Sa
Priority date: 2019-03-29
Filing date: 2020-03-30
Publication date: 2020-10-08
Also published as: JP7503073B2; US20220168068A1; JP2022526275A; EP3946138A1; EP3946138B1

Abstract

The present invention relates to a transmission rotor for a handpiece (1) intended for dental or surgical applications, comprising a device for clamping a milling tool (100) that can be rotated about an axis of rotation (R) via a drive mechanism that comprises a drive shaft (2) rotatable about the axis of rotation (R). The clamping device comprises a collet chuck (4) arranged inside the drive shaft (2) in order to axially hold the milling tool (100) relative to the axis of rotation (R), the chuck (4) cooperating with a pusher (5) to release the milling tool (100), and a guide bush (3) for radially guiding the milling tool, secured in rotation with the drive shaft (2), and it is characterised in that it comprises a mechanism for selective angular coupling (Cs) between the chuck (4) and the guide bush (3) and/or, directly, the drive shaft (2), depending on the preferred coupling mode chosen; the mechanism for selective angular coupling (Cs) applying an angular retaining torque (C) between the chuck (4) and the guide bush (3) or, respectively, the drive shaft (2), the value of which is lower than the slip threshold between the chuck (4) and the milling tool (100).

Description

Selective coupling device for a collet chuck

Technical field of the invention

The present invention relates to the field of turbines and contra-angles, more particularly to devices for clamping a milling tool.

State of the art

Most high-speed dental handpieces on the market, i.e. turbines (supplied with air) and multiplier contra-angles (supplied by electric motors) are equipped with a clamping system of the cutter based on the use of elastic grippers. This system has been well known for a very long time, in particular from the solution described in patent document EP0273259B1.

In tightening systems of this type, the rotor shaft (on which and outside of which the turbine is driven out, in the case of an air turbine, or the transmission pinion, in the case of a contra-angle) driving the rotating milling tool contains a collet and a pusher. The clamp is generally driven out and / or welded into the shaft, and it has two functions: that of axially retaining the cutter, thanks to the ends

elastic bands, and that of guiding the bur radially, to prevent, in the presence of the radial load applied by the dentist during the milling, the bur is excessively inclined and can generate excessive vibrations detrimental to the precision of the work. The pusher is itself partially free in the shaft because it can slide axially in the shaft and in certain cases rotate angularly in the shaft (in the case of a conical tappet); it cooperates with the clamp in the opening phase of the clamp to release the bur when the dentist presses the release button which covers the pusher. When the clamp is closed and retains the cutter, the pusher can simply rest on a surface of the clamp but it must never exert an opening force on the elastic parts of the clamp. In order to prevent that during milling and due to excessive axial load applied by the dental surgeon on the bur, the bur may slide past the jaws of the collet towards the cover and jam the plunger, thus making impossible for the user to push the pusher through the pressure applied to the cover and open the clamp to extract the cutter at the end of the work, there are also improved clamping systems comprising an additional component which is referred to as being a clamping stop. Such a component is introduced, preferably driven out and / or welded into the shaft on the side of the cover of the head of the handpiece, and it makes it possible to avoid any axial blocking of the pusher. The presence of the clamping stop thus limits market returns due to a milling cutter stuck in the clamping.

Furthermore, in order to be able to optimize the guiding and clamping properties of the clamp, there are also systems in which a guide bush is formed separately from the clamp; these two parts then being joined together in general by welding or brazing so as not to form more than a single block integral in rotation with the rotor shaft. In such a case, an additional component is then inserted into the shaft, near the exit of the cutter. Such a solution makes it possible to use dissociated materials which are the most suitable both for the clamp, requiring flexible and elastic materials to clip the rear end of the cutter, and for the guide bush, requiring for its part rather hard and wear-resistant materials.

However, none of these solutions of the state of the art makes it possible to effectively avoid premature wear of the clamp, due to the separation between the cutter and the clamp during a rotation under load, that is to say when this is being used by the dentist. The repeated and prolonged sliding of the milling cutter inside the collet is perhaps due in particular to the instantaneous blocking of the milling cutter involving, because of the non-negligible inertia of the rotor, the exceeding of the maximum torque provided by the clamping. Document US2014 / 154642 relates for example to a clamping device aimed at improving the centering of the milling tool by means of a support ring cooperating with the pusher mechanism in order to release and insert the tool. Such a ring is however still integral with the housing in which it is inserted, as is the collet, which is coupled, according to a preferred embodiment, via lugs to a guide sleeve provided with fixing notches, it -even also integral in rotation with this housing. Thus, more particularly, an angular connection is always ensured between the clamp and its housing. The operating constraints mentioned therein in terms of the retaining force of the milling tool thus only concern the clamping / loosening mechanism of the pusher, but not that of the securing in rotation of a drive shaft with respect to the clamp, which is sought here to keep permanently, even in the event of blockage of the cutter. Thus, no slipping of the cutter in the collet can be prevented here either.

Document EP1716817 relates to a modular clamping assembly comprising a carrier sleeve (“Tragerhülse”) in which are inserted in particular a collet (“Spannhülse”) and a guide bush (“Zwischenhülse”). The gripper and the barrel are mounted integral in rotation with a drive shaft ("Innenlagerlagerhülse"), itself integral with the rotor, via this sleeve. Nevertheless here again, since the guide bush is still integral in rotation with respect to the housing sleeve, on the one hand, and the clamp is also welded to this sleeve, it is impossible for a decoupling in rotation can never occur between these two elements. On the contrary, only a separation of the bush from the drive shaft is provided for when the latter is replaced.

Moreover, as the connection between the bush and the shaft

drive is carried out in particular via gluing in respective grooves provided for this purpose in addition to driving in, here again the blocking of the cutter is undoubtedly accompanied by a sliding of the latter in the clamp due to a lower retaining force than that corresponding to the release threshold of the sleeve with respect to the rest of the mechanism drive - otherwise you would have to change the bushing every time the cutter is blocked!

Document FR2557220A1 relates to another clamping mechanism of conventional configuration where the clamping jaws are separated from a housing sleeve constituting a drive shaft to make it a modular wear part. A preferred embodiment for this invention consists in encircling the clamping jaws by a spring ring mounted around the sleeve, in order to be able to finely adjust the clamping force. However, as in the solution disclosed in document US2014 / 154642 discussed above, the clamping jaws are always systematically integral in rotation with the sleeve when the latter is itself driven in rotation.

As explained in the description of this document, this solution aims to dispense with elastic elements for tightening by replacing them with rigid and very hard parts in order to reduce their wear and limit their replacement. This confirms that the wear is again caused by the friction between the milling tool and the jaws in the event of a jam.

DE4324493A1 otherwise discloses another solution in which a collet ("Spannzange"), having two elastic ends, is also arranged as a separate part of a guide bush. This is mounted here on a retaining ring ("Haltering"), which is itself attached to a drive shaft ("Antriebshülse").

However, this solution relates to a mechanism for clamping and respectively releasing the milling tool via the actuation of the pusher opposite to the traditional operating mode, because the clamping of the milling cutter is due to the deformation of the clamp induced by a spring. actuating the compression sleeve of the collet towards the push button. Therefore, the collet fixes the milling cutter when the collet is under the pressure exerted by the sleeve (towards the push button) and by the barrel (towards the milling cutter), while it releases the milling cutter when said collet is in absence of pressure. The mutual coupling thresholds in rotation of the different parts of the drive mechanism of the cutter in operation are not mentioned but this construction imposes whatever happens that the tightening torque of the collet on the cutter is always proportional to the tightening torque exerted by the sleeve and by the barrel on the collet . It is therefore impossible for the clamp to be detached from the barrel for a torque that is substantially less than the torque for disconnection between the cutter and the clamp. Moreover, the clamping force of the jaws of the collet is supposed to correspond simply to the usual values, and no indication is provided except on the means of alleviating problems of possible slippage of the cutter in the collet which may occur during a blockage either.

There is therefore a need for solutions free from these known limitations.

Summary description of the invention

An object of the present invention is thus to propose a new clamping device which is more efficient and makes it possible to minimize the risks of disconnection in rotation between the cutter and the clamp.

Another objective of the present invention is to provide an improved clamping device which nevertheless remains compatible with standard handpiece heads, and which does not make the operations of mounting the push-button used for loosening more complex.

These objects are achieved by virtue of the features of the main claim, and in particular by virtue of the selective angular coupling mechanism between the gripper and the guide bush or respectively the drive shaft directly, the selective angular coupling mechanism exerting a torque of angular retention between the gripper and the guide bush and / or the drive shaft, the value of which is less than that corresponding to the sliding threshold between the gripper and the milling tool. One advantage of the proposed solution is that it makes it possible to minimize the risks of separation between the cutter and the clamp, and thus to considerably improve the life of the clamping device.

At the same time, the proposed solution makes it possible to improve the reliability of the tightening while minimizing the additional components to be introduced into the construction of the handpiece, nor having an influence on the assembly operations of the latter.

According to a preferred embodiment, the selective angular coupling mechanism uses a magnetic coupling between the clamp and the guide bush, so that the magnetic force of attraction between these two parts makes it possible in parallel to position and axially hold the parts in position. mutual contact without requiring additional parts. According to a preferred variant, a magnetic ring is surmounted and secured to the guide bush as a modular part, in order to be able to choose more freely the material of the guide bush itself, and thus not to be detrimental to the guide properties imparted.

According to another preferred embodiment, the selective angular coupling mechanism uses a friction coupling via a radial clamping ring integral in rotation with the drive shaft, like the guide bush, and which would be mounted on a part. lower part of the clamp via greasy tightening, i.e. an adjustment that does not exert a retaining torque that is too great to allow relative movement between these two parts beyond the exertion of a torque in torsion going beyond a certain threshold falling within the usual operating ranges. In this case, the friction surfaces are preferably radial and cylindrical, and the coupling takes place directly between the clamp and the drive shaft. Furthermore, according to a preferred variant for this purely mechanical coupling mode, the shape of the clamp may have a lower flange forming an axial retaining surface, or even a peripheral bead in a more intermediate part, which can then be covered with a additional clamping ring

also incidentally fulfilling the function of axial locking, and increasing otherwise the contact surface for the exercise of a friction torque, and consequently the adjustment of the value of the retaining torque with respect to the clamp.

According to yet another preferred embodiment, the pusher is made in two parts, one of which is fixed in rotation with respect to the drive shaft and therefore of the guide bush, and the other, cooperating with the clamp. , is mounted completely free in rotation in the drive shaft. Such a variant has the advantage that the clamp can slide for a long time on the barrel, when these two parts are made to be separated, without however generating any risk of opening of the pusher due to the torsion exerted on the jaws, especially when the latter take the form of two legs arranged in diametrically opposed fashion. According to a particularly advantageous variant, the lower part of the pusher free to rotate in the shaft is conical.

Brief description of the drawings

The present invention will be better understood on reading the description which follows, given by way of example and made with reference to the drawings in which:

- Figure 1 is a front view of the head of a handpiece provided with a milling tool according to a preferred embodiment for the present invention;

- Figure 2 is a partial sagittal sectional view, along the sectional plane (SS) shown in Figure 1, in three dimensions of a handpiece using a transmission rotor provided with a movable wheel of turbine, which is often referred to more simply as “turbine rotor” provided with a clamping system with selective coupling in rotation according to a preferred embodiment for the present invention;

- Figure 3 shows an enlarged sectional view of the handpiece of Figure 2 in the sagittal plane (SS); - Figure 4 is a partial sagittal sectional view in three dimensions of a handpiece using a turbine rotor provided with a clamping system with selective coupling in rotation according to another method of

preferred embodiment for the present invention; - Figure 5 shows an enlarged sectional view of the handpiece of Figure 5 in the sagittal plane (S-S);

- Figure 6 is a partial sagittal sectional view in three dimensions of a handpiece of the contra-angle type no longer using compressed air but an actuation via a motor shaft, and which is provided with a transmission rotor equipped with a tightening system with selective coupling in rotation according to yet another preferred embodiment for the present invention;

- Figure 7 shows an enlarged sectional view of the handpiece of Figure 8 in the sagittal plane; - Figure 8 shows the detail of a purely mechanical selective coupling mechanism according to another preferred embodiment for the present invention, still in a sagittal sectional view;

- Figure 9 shows the detail of a selective coupling mechanism according to yet another preferred embodiment for the present invention according to the same sagittal sectional view as in Figure 8;

- Figure 10 shows the detail of a selective coupling mechanism according to yet another preferred variant for the present invention according to the same sagittal sectional view as Figures 8 and 9.

Detailed description of the invention In the context of this application, the handpiece in which the clamping mechanism according to the invention can be integrated can equally well consist of a "turbine", when the milling cutter is rotated under the action of compressed air injected through a duct, or in a “contra-angle” using a drive shaft actuated by a motor, called the motor shaft.

A view of the exterior of a handpiece 1, which may consist of a turbine or a contra-angle, is precisely illustrated in FIG. 1. It comprises a head 10 at the bottom of which is inserted the bur 100, rotatably mounted around its axis of rotation R. A push button 61 covering the head 10 conventionally allows, when pressure is exerted on it by the user of the handpiece, that is to say typically the surgeon -dentist, to release the bur 100. The arrows SS in figure 1 show the sagittal cutting plane will be used in the following figures 2 to 8 to allow a more detailed view of the mounting and clamping mechanism of the bur 100 proposed. in the context of the present invention, first of all in the context of a turbine (in Figures 2 to 5) then in the context of a contra-angle (Figures 6 and 7). In what follows, we will first describe a first preferred embodiment linked to a turbine, in connection with Figures 2 and 3.

Figure 2, which consists of a partial sagittal sectional view in three dimensions of a handpiece 1 along the section plane (SS) shown in Figure 1, makes it possible to distinguish the various usual elements of a head 10 and a clamping mechanism for the milling cutter 100 - however not shown for the sake of clarity - including in particular the duct

compressed air supply 11 on the right of the figure, driving the turbine wheel 21, itself integral in rotation with a drive shaft 2 for the milling tool 100, which is commonly referred to as being "Rotor shaft". On the drive shaft 2 are inserted here two

bearings 23, preferably ball bearings, themselves compressed by respective O-ring 24 type seals. In the drive shaft 2 are respectively mounted the clamp 4 for axial retention of the cutter - whose jaws are not visible in this figure, but better visible in Figure 7 relating to the embodiment corresponding to a contra-angle - and the radial guide barrel 3, these two parts being separated to be able in particular adjust the materials used for the clamp 4 to those of the guide barrel 3. In fact, while the clamp 4 requires materials which are preferably elastic and deformable, the barrel 3 preferably requires very hard materials, so as to be wear-resistant and guarantee excellent guiding properties along the axis. rotation R as long as possible.

In the upper part of the head is inserted a retaining part for the push-button 61, which is provided to release the milling cutter 100. This retaining part consists, according to the preferred embodiment described, of a nut 62 screwed into the nut. head by means of a threaded bead 621 at its outer periphery, cooperating with an internal thread 13 formed in the head 10; a seal 64 is provided at the level of the cooperation of these screwing surfaces in order to ensure the repeatable positioning of the nut and the push button and, in the case of a turbine, thus to stabilize the aerodynamic flows coming out of the head. On top of the retaining nut 62 is disposed a spring 63 making it possible to return the push-button 61 without its rest position, as shown in Figures 2 and 3, where a radial peripheral hooking part 612 of the push-button is held in abutment against an internal peripheral retaining spout 622, the cooperation of the hooking parts being demonstrated in FIG. 3. In FIG. 2, one can also distinguish, at the level of the lower face 610 of the push-button 61, an anti-heating ball 8, made of a material with low thermal conductivity provided for this purpose, and which is preferably driven directly into a central housing 613 arranged in the push-button 61, here of hexagonal section in order to minimize the thermal bridges of heat transfer towards the push-button 61.

The push module 6, formed by the nut 62 and the push button 61, as well as the compression spring 63 interposed between the two, is illustrated later in FIG. 3. In FIG. 2, it is nevertheless possible to now and already distinguish the push-button 5, with which the push-button 61, or here more exactly the ball 8, can be brought into contact, when a pressure is exerted in the direction P, visible in Figures 3 and 4, and a permanent clamping magnet 7 arranged in the nut 62. In the context of the present invention, the pusher 5 is made of a passive ferromagnetic material, so as to cooperate with the permanent clamping magnet 7.

For a turbine, the transmission rotor therefore consists of the turbine wheel 21 at the input and the drive shaft 2 at the output, as well as the bearings 23, the clamp 4, the pusher 5 and the barrel 3.

For a contra-angle, the transmission rotor consists of a drive pinion 22 (which replaces the turbine wheel 21) at the input and the drive shaft 2 at the output, as well as the bearings 23, the clamp 4, pusher 5 and barrel 3. The power available to the transmission rotor, therefore the torque and the speed of rotation of this rotor, depends on the handpiece in which the rotor is integrated, as well as on the pipe and the compressed air supply network (in the case of the turbine) or of the motor and the motor control electronics (in the case of the contra-angle). The torque transmitted to the shaft

of drive 2 also depends on the rotational speed of the rotor of

transmission, which depends on the torque applied at the input to the tool (via compressed air in the case of the turbine, or the speed of rotation imposed on the motor for the contra-angle); the efficiency of the transmission rotor decreases sharply with increasing speed (and tends to zero for maximum speed, in the case of a turbine). However, in both cases, for the turbine or the contra-angle, the maximum torque that can be transmitted to the drive shaft 2 depends only on the input component of the drive mechanism (the turbine wheel 21 or the drive pinion 22, respectively), the friction and the performance of the bearings 23 and the mechanical connection between this input component and the drive shaft 2; the torque transmitted cannot exceed the breaking limit of this mechanical connection.

For example, for a turbine, the maximum torque that can be transmitted to drive shaft 2 - regardless of the geometry of the handpiece in which the rotor is integrated and the available air pressure - is determined by the efficiency of the bearings 23, the diameter and height of the turbine wheel and the number and shape of the blades of the turbine wheel 21.

For a contra-angle, the maximum torque which can be transmitted to the drive shaft 2 - regardless of the geometry of the handpiece in which the rotor is integrated and the available air pressure - is determined. by the efficiency of the bearings 23, and the number, material and shape of the teeth of the drive pinion 22.

Considering these technical limitations, the maximum torque Cn which can be transmitted to the drive shaft 2 via the transmission rotor is of the order of 2 to 6 mNm if the rotor is integrated into a turbine while it can generally reach 10 mNm if the rotor is integrated in a contra-angle connected to a motor rotating at a speed lower than 20Ό00 rpm.

In what follows, reference will be made indifferently to FIG. 3, using the same elements as FIG. 2 previously described in the sagittal plane SS, and FIG. 3, and which represents the various elements of the improved clamping device according to the invention. according to an enlarged view. The description of the references common to all these figures will not be systematically repeated. In Figures 2 and 3, it can be seen that a ring-shaped permanent clamping magnet 7 is positioned in the retaining nut 62 of the push-button 61 by means of a retainer 72 having a cylindrical part. 721 and an axial retaining collar 722. This part can be fixed in any way to the nut 62, for example by driving in, welding, or even screwing, and it can be noted that the positioning of the magnet 7 of annular shape radially exceeds the casing of the pusher 5, which moreover has peripheral shoulders 50 in order to be able to have the clamping stop 51. This clamping magnet 7 is magnetized in the axial direction and therefore continuously exerts a force of attraction directed substantially upwards on the partner ferromagnetic element, ie the pusher 5 of the clamping device. The magnetic force of attraction Fi is materialized by the arrow in FIG. 4 illustrating the fact that the pusher 5 is held in the upper position in the direction of the push-button 61. In conditions of use, that is to say during the rotation of the shaft d 'drive 2 and milling, this magnetic force of attraction Fi makes it possible to press the pusher 5 against the clamping stop 51, and thus prevents the jamming of the pusher 5 in the clamp 4 and the accidental opening of the latter.

The permanent clamping magnet 7 is, in the context of the present invention, preferably of annular or cylindrical shape, that is to say having a shape of revolution around the axis of rotation R of the milling cutter. According to the embodiment illustrated by Figures 2 to 4, the fact that the permanent clamping magnet 7 is positioned in the nut 62 has the consequence of bringing the latter as close as possible to its partner ferromagnetic element, that is to say - say pusher 5, and thus maximize the intensity of the force

magnetic Fi making it possible to effectively maintain it in its "high" position, that is to say where the pusher is held in contact against the clamping stop 51.

This implementation according to which the permanent clamping magnet 7 is fixed and located in the retaining nut 62 of the push button 61 also has an additional technical advantage of reliability. Indeed, during the opening of the clamping, the push button 61 is pressed by the user in direction P, to push the push button 5 inside the clamp 4 and therefore open the elastic sleeves of the clamp 4: in this case, the user must overcome not only the holding force of the spring 63 compressed between the nut 62 and the push button 61, but also the magnetic force Fi between the push button 5 and the permanent clamping magnet 7, this which adds additional security with respect to the risk of accidental pressing of the push-button 61 by the user.

In order to avoid any premature wear of the collet 4, due to the separation between the milling tool 100 and the collet 4 during a rotation under load, due in particular to an instantaneous jamming of the cutter involving, because of the 'significant inertia of the rotor, the exceeding of the maximum torque ensured by the tightening, a selective angular coupling device C _s is proposed within the framework of the invention between the gripper 4, and the barrel of guide 3, formed by two separate parts assembled in a removable and reversible manner to one another, in order to precisely allow the clamp 4 to be released from the guide bush 3 before the milling tool 100 is brought itself to turn in clamp 4. Another constraint

functional of such a modular clamp 4 mounting system on the barrel

3 consists in ensuring that the clamp never disconnects angularly from the barrel either, whatever the torque applied at the input to the shaft

training. In other words, the proposed selective angular coupling mechanism C _s must exert an angular retaining torque C between the clamp 4 and the guide bush, the value of which is between that corresponding to the maximum transmission torque Cn of said drive mechanism, and that corresponding to the slip threshold between said clamp 4 and said milling tool 100, which can be summarized by the following inequality:

Ctr C <1 Cgii _s In practice, considering that the slip threshold between the clamp

4 and the milling tool 100 is of the order of 20 to 30mNm and, as illustrated above, that the maximum torque Cn supplied to the drive shaft 2 via the transmission rotor is of the order of 2 to 6 mNm for a turbine and of the order of 10 mNm for a contra-angle], the angular retaining torque (C) will preferably be between 4 mNm and 20 mNm.

Considering that the transmission rotor is generally a spare component for turbines and contra-angles (it is therefore possible to replace only the worn transmission rotor, during a repair carried out by an after-sales service operator or, in some cases, directly by the user), it is advantageous to use the same transmission rotor to equip several models and types of turbine or contra-angle models having a different transmission ratio and / or efficiency. In this situation, when designing the transmission rotor, only the sliding torque between the collet and the milling tool is known (thanks to the fact that the milling tools are standardized), while the maximum torque supplied to the The drive shaft is not specified. In these cases, considering the torque intervals defined above, the rotor of transmission and the clamping system according to the invention should preferably be dimensioned by requiring that the angular retaining torque satisfies the relationship:

C _güs / 2 <C <C _gUs. This construction criterion ensures the correct

operation of the clamping system integrated in a universal transmission rotor, that is to say usable in several models of turbine or contra-angle.

In the embodiment illustrated by Figures 2 and 3, the coupling mode used by the selective angular coupling mechanism C _s is of the magnetic type, which also makes it possible not only to guarantee the mutual coupling in rotation between the guide bush 3 and the clamp 4, but also to ensure their axial positioning without requiring the addition of any other part to perform this latter function. In these figures, it can be seen that the guide bush 3 is surmounted by a permanent magnet of annular shape - the magnetic coupling ring 30 - which can be driven out and / or soldered and / or welded directly into the shaft. 'drive 2, or brazed and / or welded to the guide bush 3 via its lower fixing surface 302, affixed to the axial end of the guide bush 3. The guide bush 3 is still integral with the drive shaft 2 - for example by driving - while the collet 4 is on the contrary not driven into the drive shaft 2, but free to turn around the axis of rotation R of the milling tool 100.

This magnetic coupling ring 30 is magnetized in the axial direction and therefore continuously exerts a downwardly directed magnetic attraction force F2 on the partner ferromagnetic element, which in this case is constituted by the collet 4. In addition torque of magnetic origin, a torque of mechanical origin - due to mechanical friction between the parts at the level of the coupling surfaces - is exerted by the magnet on the clamp 4, opposing the rotation of the clamp 4 by relative to the guide bush 3. Thus the angular retaining torque C between the clamp 4 and the guide bush 3 results at least partially from the friction between the axial coupling surface lower 41 of the clamp 4 and the upper axial coupling surface 31 of the guide bush 3.

An advantage of this embodiment is that the guide bush 3 and the permanent magnet formed by the magnetic coupling ring 30 can be made of two different materials, favoring the hardness for the guide bush 3 and the magnetic saturation for the magnet: for example, the guide bush could be made of non-magnetic hard metal (CW), and the magnet of SmCo, which on the contrary constitutes a material which is not particularly hard and fragile.

From a functional point of view, during the milling work, the milling torque applied to the milling tool 100 is transmitted to the collet 4: in the case where the milling tool 100 is accidentally blocked by a roughness of the material being milled, the instantaneous torque exerted on the collet 4 increases

considerably because of the inertia of the drive shaft 2, which does not manage to stop quickly enough when impacted by the milling tool 100. In this case, the instantaneous torque applied to the collet 4 by the milling tool 100 exceeds the angular retaining torque C exerted by the guide bush 3 on the collet 4, which causes the assembly (collet 4 - milling tool 100) to slide relative to the bushing. guide 3. The fact that the separation of the assembly (collet 4 - milling tool 100) from the guide bush 3 occurs before the milling tool 100 is detached from the collet 4 makes it possible to preserve the collet from the phenomena of 'wear caused by friction of the milling tool 100 in the collet 4.

Another important property of the clamping system according to the invention can be well understood in this embodiment: as a result of the phenomenon which caused the assembly (clamp 4 - milling tool 100) to become detached from the guide bush 3 and / or of the drive shaft 2, the selective coupling between the clamp 4 and the guide bush 3 and / or the drive shaft 2 is restored without any degradation or wear, that is to say that the holding torque is not modified when the disconnects

components. In practice, the number of times the phenomenon of

temporary separation of the assembly (collet 4 - milling tool 100) from the Guide bush 3 and / or the drive shaft 2 occurs has no negative impact on the service life of the clamping system and the transmission rotor. This phenomenon of separation cannot even be perceived directly by the user. Figures 4 and 5 illustrate another preferred embodiment for the present invention, still relating to a turbine.

According to this embodiment, the drive device of the cutter 100 is in all respects identical to that of the described embodiment

previously and illustrated by Figures 2 and 3; therefore, all references introduced within the framework of these figures will not be explained again.

However, the clamping device of the cutter 100 has a different arrangement from the permanent magnet 7, which this time is no longer integrated in the nut 62, but directly in the push button. Indeed, as can be seen in Figure 5, a permanent clamping magnet 7 of annular shape is this time arranged around the housing 613 of the anti-heating ball 8, in a recess 611 in the lower face 610 of the button. pushbutton 61. It is held in position inside the recess of pushbutton 61 by an axial retaining washer 71, preferably welded or glued to pushbutton 61. The ferromagnetic element partner of the magnet is always the pusher 5, shown in Figures 4 and 5 in the 'high' position, that is to say held in contact against the clamping stop 51 thanks to the magnetic attraction force Fi materialized by the arrow visible on the Figure 7 and tends to pull the pusher 5 upwards.

The operating mechanism is similar to that of the previous embodiment in the rotation / milling phase, where the pusher is attracted upwards following the magnetic attraction force Fi exerted by the magnet. Nevertheless, a major difference can be observed when pressing the push-button 61, illustrated by the arrows P in FIG. 5. In fact, during such a phase of pressing on the push-button 61, the magnetic attraction this time will favor the descent of the push-button 61 because of the distance between the permanent clamping magnet 7 which decreases when the button- pusher approaches pusher 5. Consequently, the intensity of the pressure P which must be applied by the user is less than in the absence of a magnet, whereas it was increased in the previous case.

However, since in the embodiment of Figures 4 and 5, the permanent clamping magnet 7 is in a position further from the pusher 5 than in the embodiment of Figures 2 and 3, the force

magnetic attraction Fi exerted on the pusher 5 will be less, equal in dimensions of the permanent clamping magnet 7 and the pusher 5. This last embodiment of Figures 4 and 5 is on the other hand easier to achieve, because A simple washer can be used to line the permanent clamping magnet. Moreover, in order to increase the magnetic force exerted on the pusher 5, it would also be possible to produce the axial retaining washer 71 also in a ferromagnetic material, as well as the anti-heating ball 8, for example made of tungsten carbide. with a 30% Cobalt content.

In a particularly advantageous variant of the embodiments illustrated in FIGS. 2 to 5, the clamping stop 51 is also free to rotate in the drive shaft 2, like the clamp 4. In other words: this clamping stop 51 is not driven and / or welded, which makes it possible to withstand particularly long temporal transients during which the clamp 4 slides on the guide bush 3 without the risk that the pusher 5 may force the opening of the clamp 4 by the 'exertion of forces resulting in a torque on the clamping jaws. In this case, the clamping stop 51 is placed in the drive shaft 2 and the crimping of the upper periphery of the drive shaft 2 ensures that the clamping stop 51 cannot come out axially from the drive shaft 2.

According to a variant illustrated by FIGS. 6 and 7 which follow, relating to a contra-angle, the permanent clamping magnet 7 could also take the form of a disc or of a pellet positioned inside the push-button. , but behind the anti-heating ball 8. In such a case, the thickness of the permanent clamping magnet 7 could also be increased so

considerable to result in an increased magnetic attraction force Fi. Figures 6 and 7 show a different drive mode of the rotor shaft, that is to say the drive shaft 2, compared to the turbine of previous Figures 1 to 7, this time by means of a gear between the motor shaft 12, driven by an electric motor, and the drive pinion 22 which replaces the turbine wheel 21 in the transmission rotor. The pusher 5 is now made in two parts, with an upper part 52 of the pusher 5 which is integral in rotation with the drive shaft 2, due to the stopping of the pusher 51 formed by a transverse pin, and a part lower conical 53 free to rotate relative to the drive shaft. The permanent clamping magnet 7 formed by the pellet arranged in the recess 611 of the lower face 610 of the push button 61 is now capable of coming into contact with the anti-heating ball 8.

this time no longer fitted directly into a housing of the push-button 61, but on the upper part 52 of the push-button 5. As can be seen in FIG. 7, which constitutes a

enlargement of FIG. 6 in the sagittal sectional plane SS, the jaws 45 of the clamp 4 axially retain the bur 100 (not shown for reasons of legibility of the other parts) as long as the conical lower part 53 does not move them apart when 'pressure is exerted on the push button 61 towards the interior of the head 10, in accordance with the direction of the arrow referenced "P". In such a case, the passive magnetic element associated with the permanent clamping magnet 7 housed in the recess 611 arranged on the underside of the push-button 61 consists precisely at least of the conical lower part 53, and, due to the axial distance of this part from the permanent clamping magnet 7, potentially also the upper part of the pusher 5.

In the contra-angle illustrated by Figures 6 and 7, it can be seen that the embodiment of the selective angular coupling mechanism C _s is similar to that of Figures 2 and 3, involving a magnetic coupling mode and where a ring of Magnetic coupling 30 is interposed between the guide bush 3 and the clamp 4. All the references explained in detail in the context of the description of Figures 2 and 3 will therefore not be repeated here. However, as explained above, the pusher 5 is now split into two parts with an upper part 52 blocked in rotation by a transverse pin used as a clamping stop 51, and a conical lower part 53 free to rotate in the shaft d. 'drive 2, which also makes it possible to avoid forcibly opening the jaws 45 of the clamp 4 by exerting a torque, as well as causing wear of the pusher 5 due to friction when the clamp 4 would be caused to rotate in the drive shaft, which, in the long term, could generate a slight inclination of the pusher 5 and consequently its locking in the axial direction.

In the foregoing, we have described the production of magnetic couplings for the selective angular coupling mechanism C _s , which has the following advantages:

- Harness non-contact forces, which reduces or eliminates the effects of wear;

- Ensure the efficiency of the technical solution regardless of geometric dimensions.

- Minimize the number of additional components to be introduced into the construction of the handpiece.

- Do not complicate assembly operations compared to typical constructions.

However, in the context of the present invention, a purely mechanical coupling, that is to say by friction, can also be carried out, in particular via a teflon or bronze ring, inserted and driven into the drive shaft and inside which the clamp 4 is driven out with a low driving force (also called "fat driving", which ensures a relatively low retaining torque of the clamp).

Figures 8 to 10 show different preferred embodiments for a selective angular coupling mechanism (C _s ) according to the invention using such a coupling mode, using in particular radial surfaces between the clamp 4 and directly the drive shaft 2. For all these figures, the references common to all the usual parts of the clamping device (in particular the drive shaft 2, pusher 5 and clamping stop 51, guide bush 3, clamp 4 and its clamping jaws 45) and the coupling surfaces between the bush and the clamp will only be introduced for the description of figure 8 but not repeated for later figures.

FIG. 8 thus shows for example a drive shaft 2 in which is mounted a guide bush 3, for example by driving or welding, and a clamp 4 whose clamping jaws 45 are capable of being separated by a pusher 5, which is mounted a clamping stop 51 as in the configurations described above. An essential difference in this mode of coupling compared to those described

previously is that it no longer takes place between the guide bush 3 and the clamp 4, but directly between the drive shaft 2 and the clamp 4 thanks to the presence of the radial clamping ring 9 which is preferably driven into the drive shaft 2 or welded to the latter. This radial clamping ring 9, affixed to the axial end of the guide bush 3, requires a modification of the shape of the clamp, which then has a shoulder 43 resting on the upper surface 93 of the radial clamping ring 9 , while the internal radial coupling surface 92 cooperates by friction with the external radial coupling surface 42 of the clamp 4. In this way, not only an angular retaining torque C is ensured between the radial clamping ring 9 and the clamp 4, but an axial retaining force is

at the same time exercised to guarantee their mutual solidarity. For the sake of completeness, it will be noted that frictional forces are also exerted at the level of the upper coupling surface of the barrel 31 and of the lower coupling surface of the clamp 41; nevertheless, in view of the ratio of this surface to the radial clamping surfaces mentioned above, the contribution of this friction could be considered as negligible, as well as that occurring at the level of the coupling between the upper surface of the ring 93 serving as support on the lower shoulder of the clamp. Consequently, to increase the friction surfaces, the embodiment illustrated in FIG. 9 proposes adding an additional radial clamping ring 9 above a radial peripheral bead 44 positioned above the first radial clamping ring. 9 previously described; the shape of the lower surface 443 of this bead corresponding to the lower peripheral shoulder of FIG. 8, while the outer surface of the bead 442 is flush with the inside of the drive shaft 2. Here again, the coupling in rotation between the clamp 4 and the drive shaft 2 - and therefore the guide bush 3 in parallel - is ensured by the cooperation by friction between the internal radial coupling surface 92 and the external radial coupling surface 42 of the clamp 4 , but now another cooperation by friction is ensured between a second internal radial coupling surface 92 'of the additional radial clamping ring 9', also secured to the drive shaft 2. According to this preferred embodiment aimed at increase the friction surfaces, we can maintain the hypothesis that the contribution of the cooperation between the upper coupling surface of the barrel 31 and the lower coupling surface of the clamp 41 to the retaining torque angular C always remains negligible, as do those of the other surfaces of the two clamping rings 9 and 9 'used. However, this solution has the advantage of offering an axial stop for the positioning of the clamp 4 by means of the lower surface 92 ′ of the additional radial clamping ring which is superimposed on the upper surface 441 of the radial peripheral bead 44 ; moreover, such a variant according to which the clamp 4 having a

radial peripheral bead shoulder 44 interposed between a first radial clamping ring 9 and an additional clamping ring 9 ’further improves the guidance of the clamp in the drive shaft 2.

For the clamping device relating to the embodiments illustrated by FIGS. 8 and 9, the sub-assembly constituted by said clamp 2, the guide bush 3 and the radial clamping ring 9 can be assembled outside the shaft d 'drive (2) and then driven into the latter, in order to be able to test the angular coupling properties in a modular fashion.

FIG. 10 finally illustrates a variant according to which the clamp 4 is provided with a lower flange 40 wedged under the radial clamping ring 9, the lower surface 92 of which acts as an axial stop by bearing against the upper surface 401 of the lower flange 40. However, similar to the embodiments of FIGS. 8 and 9 above, the rotational coupling between the clamp 4 and the shaft d drive 2 is provided by the

cooperation by friction between the internal radial coupling surface 92 of the radial clamping ring 9 and the external radial coupling surface 42 of the clamp 4.

According to variants not shown, one or more O-ring type seals could be introduced between the clamp 4 and the drive shaft 2 in order to replace or complement the radial clamping ring 9 for retaining the clamp 4 according to requirements. needs.

Similarly, elastic lamellae can be introduced (then driven out or welded or glued) in the drive shaft 2 (through openings previously machined in the drive shaft 2), and be brought to bear on the outer surface of the clamp 4 to ensure the same function of retaining the clamp provided by the radial clamping ring 9.

According to all the embodiments illustrated above relating to the clamping device, the clamp 4 can be coated, on the outer surface, with DLC, acting as a self-lubricating coating, which makes it possible to minimize friction and therefore improve service life. . Furthermore, the clamp 4 can advantageously be manufactured, when it is made of a flexible plastic material, by 3D printing in order to optimize its properties

geometric.

In the foregoing, we have thus described a selective angular coupling mechanism C _s which allows:

- A reduction in the wear mechanisms of the clamp 4;

- A reduction in the risk of accidental exit of the milling tool 100 during the work of the dentist. - The possibility of increasing the torque and power of the handpieces without reducing their reliability or service life.

Although the invention relating to this new improved clamping device with selective angular coupling mechanism C _s between the clamp 4 and the guide bush 3, has been described in connection with distinct embodiments illustrated by the sets of figures which above, it will be understood that a combination in particular of the preferred embodiments relating to the modes of coupling between the guide bush 3 or respectively the drive shaft and the clamp 4, namely magnetic and respectively

mechanical, could be combined, and that the integration of the clamping devices can either be carried out in a turbine or a contra-angle as required.

Claims

1. Transmission rotor for handpiece (1) intended for dental or surgical applications, comprising a mechanism

drive in rotation of a milling tool (100) comprising bearings (23), a turbine (21) or a drive pinion (12) as input, and a drive shaft (2) rotating around it 'an output axis of rotation (R), said drive shaft (2) being adapted to actuate said milling tool (100) in rotation about said axis of rotation (R), as well as a clamping device a milling tool (100), said clamping device comprising a clamping collet (4) disposed inside said drive shaft (2) for axially maintaining said milling tool (100) with respect to said axis of rotation (R), said clamp (4) cooperating with a pusher (5) for releasing said milling tool (100), as well as a radial guide bush (3) of said milling tool, integral in rotation with said shaft d 'drive (2), characterized in that said clamping device comprises a selective angular coupling mechanism (C _s ) between said clamp (4) and edit guide bush (3) and / or said drive shaft (2), said selective angular coupling mechanism (C _s ) exerting an angular retaining torque (C) between said clamp (4) and said guide bush ( 3) and / or said tree

drive (2) whose value is less than the slip threshold between said clamp (4) and said milling tool (100).

2. Clamping device according to claim 1, characterized in that the angular retaining torque (C) being between 4mNm and 20mNm.

3. Clamping device according to claim 1 or 2, characterized in that said selective angular coupling mechanism (C _s ) between said clamp (4) and said guide bush (3) and / or said drive shaft (2) uses a magnetic coupling between said clamp (4) and said guide barrel (3) integral in rotation with the drive shaft (2).

4. Clamping device according to claim 3, said clamp (4) being made of a passive ferromagnetic material and said guide bush (3) consisting of a permanent magnet.

5. Clamping device according to claim 4, the angular retaining torque (C) between said clamp (4) and said guide bush (3) and also resulting from the friction between the lower axial coupling surface (41) of said clamp (4) and the upper axial coupling surface (31) of said guide barrel (3).

6. Clamping device according to claim 3, said clamp (4) being made of a passive ferromagnetic material, and said guide bush (3) being surmounted by a magnetic coupling ring (30).

7. Clamping device according to claim 6, the angular retaining torque (C) between said clamp (4) and said guide bush (3) and / or the drive shaft (2) also resulting from the friction between the lower axial coupling surface (41) of said clamp (4) and the upper axial coupling surface (301) of said magnetic coupling ring (30).

8. Clamping device according to one of the preceding claims, characterized in that said selective angular coupling mechanism (C _s ) between said clamp (4) and said guide bush (3) and / or said drive shaft (2 ) uses a friction coupling between a radial clamp ring (9) mounted on said drive shaft (2) and said clamp (4), a lower radial coupling surface (91) of said ring (9) being in contact with an outer radial coupling surface (42) of said clamp (4).

9. Clamping device according to claim 8, characterized in that said clamp (4) has a lower flange (40) at its base having an upper peripheral surface (401) of axial stop arranged under the lower axial retaining surface (92). of said radial clamping ring (9).

10. A clamping device according to claim 8, said clamp (4) having a radial peripheral bead shoulder (44) interposed between said radial clamping ring (9) and an additional clamping ring (9 ').

11. Clamping device according to one of the preceding claims, said pusher (5) being provided with a radial peripheral shoulder (50), and being surmounted by a clamping stop (51) mounted to rotate freely in the shaft. drive (2).

12. Clamping device according to one of the preceding claims, said pusher (5) being furthermore formed of an upper part (52) integral in rotation with said drive shaft (2), and of a lower part (53). ) conical cooperating with said clamp (4) free to rotate inside said drive shaft (2).

13. Clamping device according to one of the preceding claims, said clamp (4) being coated, on the outer surface, with a self-lubricating coating such as DLC.

14. Clamping device according to one of the preceding claims, said clamp (4) being made of plastic material by 3D printing.